1. Field of the Invention
The present invention relates to mechanical presses, and more particularly, to a detector and detection method for determining when a drive piston in a press has deviated from a preferred reciprocating drive path, the detector thereby preventing undue damage to the press guiding system and the drive piston when sufficient clearance is lost.
2. Description of the Related Art
Mechanical presses are frequently used in forging, forming, bending, blanking, or otherwise shaping material such as metal. Mechanical presses generally include a stationary bed and a vertically reciprocal ram driven by a piston. A die is mounted to the stationary bed, and a complimentary die is mounted to the reciprocating ram. When driven together, the two dies form the material to the shape of the dies. The formed material is subsequently removed from the press, and a new sheet of material inserted.
The accurate guiding of the press slide during reciprocation thereof is highly important because if the dies mounted on the press bed and the press slide are not held in proper registration, improper workpieces are produced and damage to the press parts and dies could potentially result. Furthermore, it is not always the case that the dies of the aforesaid nature can be mounted in a press in such a manner as to prevent any non-uniform loading on the press slide, and when such loading occurs, a press slide may be subjected to rather large forces in the side to side or fore and aft directions, thereby tending to thrust the slide laterally in one direction or the other.
Under circumstances of this nature, guide surfaces of the press slide and press frame wear excessively, and improperly formed workpieces can result. Typically, it is when this clearance is lost or reduced below tolerance that the drive piston""s lubricating oil film is squeezed out, and the piston consequently begins to damage the guide members. If these types of problems go undetected, a loss of production can result in addition to substantial downtime for the press.
Having the foregoing in mind, it is a primary object of this invention to detect when a drive piston and guide member loses the clearance between them, and prevent further damage to both press components. By recognizing such a fault and immediately ceasing operation of the press, press downtime is reduced, as well as the cost of repair and replacement parts.
The present invention is directed to a detection system for detecting when a drive piston contacts the guide member. The invention includes a contact element having an electrical potential of between positive 12 and 24 VDC, and a negative ground that is connected to the drive piston, such that when the drive piston deviates from its preferred drive path, it makes contact with the contact element, thereby decreasing the electrical potential in the contact element. The invention further comprises a responder that responds to the decrease in the electrical potential by indicating the fault to the press operator or press controller and simultaneously shutting the press down.
The invention provides for the contact element to be located in the lower part of the guide member. During normal operation, a drive piston passes over the contact element without coming into contact with it. However, when the press is improperly adjusted, or the guiding member or clearance has become ineffective or lost, the drive piston comes in contact with the guide, and subsequently contacts the contact element.
In an alternative embodiment, the contact element is replaced with an eddy current sensor, which does not require direct contact by the piston, but rather senses when the piston is near enough to create an eddy current.
In the preferred embodiment of the invention, the drive piston is at ground electric potential. The contact element holds a positive 12 to 24 VDC electrical potential. As long as the voltage remains constant at this contact element, the press can operate normally. However, when the piston deviates from its preferred path, and touches the detector, the positive 12 to 24 VDC will suddenly decrease, signaling to the responder to indicate a fault and shut down the press operation.
In the invention, an electrical characteristic is applied to a driven member of the press, and a detection element with an electrical characteristic is secured to the guide member of the press, such that the detection element experiences a detectable change in its electrical characteristic when it is engaged with the driven member. A responder subsequently responds to the change in electrical characteristic by signaling a fault and to cease operation of the press.
In an alternative embodiment of the invention, an eddy current sensor element is secured to the guide/member of the press, the eddy current sensor element signaling to a responder when the driven member deviates from its reciprocation path.
The invention can also be stated as a method comprising the steps of providing a ground electrical characteristic to a drive piston, and providing a contract element mounted to a guide member for contacting the drive piston when the drive piston is horizontally translating during press operation.
It is an advantage of this electrical system there are no complicated sensors or moving parts of the detectors that can fault or break.
It is a further advantage of the system that the operator can be immediately notified of undesirable operation. Prior to this invention, operation of the press in this loss of clearance condition could sometimes go undetected until problems would occur in the tooling or a seal would prematurely fail.